[Soul Engineering]

Boost leaks? That's generally the cause. What fuel pressure regulator and does fuel pressure rise as boost comes in?

I'd bet it's either boost leaks or ignition break up. I'm wondering how the tuner got past the code? Probably just disabled it, which isn't really helping. Convert the dizzy to OBD1 or go coil on plug and I'd bet the issue goes away.

 

[Soul Engineering]

Can we have a look at the timing maps on the tune? Download S Manager if you haven't already, pull up the timing maps and let's have a look see. I'd bet there's probably 12-14 degrees of timing in it which will literally kill it. Power wise and internally as well.

 

[Soul Engineering]

If you fixed boost leaks and suspect more, it will need more tuning. Surprised the tuner didn't check for boost leaks. Have you checked to see how freely the turbo spins by hand? Or to see if there is any shaft play.

But yes, you need to pull timing out of that tune, because once you do find the issue, fix it and then go for a rip, it might pop the head gasket, or do bottom end damage.